Refactor tagging and add library scanning

- Replace `Tag` class with utility helpers for hashing and file type parsing
- Change `Track.artwork` from `std::string` to `TagLib::VariantMap`
- Add `importArtwork`, rename `importFolder` to `scanFolder`
- Add `scanLibrary`, `updateLibrary`, `editMetadata`, and `seek` methods to `Player` hierarchy
- Remove obsolete `Tag.h`/`Tag.cpp` files

include/utility.h

@@ -0,0 +1,11 @@
+#pragma once
+
+#include "Containers.h"
+#include <cstdint>
+
+namespace utility {
+
+    uint64_t hashString( const std::string& s );
+    std::string parseFiletype( const std::string& filePath );
+
+}